Spark ignition systems for internal combustion engines



March 12, 1968 B. L.. PHILLIPS ETAL 3,372,682

SPARK IGNITION SYSTEMS FOR INTERNAL COMBUSTION ENGINES Filed March 8, 1966 ow mv United States Patent OfiFice 3,372,682 Patented Mar. 12, 1968 3,372,682 SPARK IGNITION SYSTEMS FOR INTERNAL COMBUSTION ENGINES Brian Leslie Phillips and Derek Stanley Adams, Birmingham, England, assignors to Joseph Lucas (Industries) Limited, Birmingham, England, a British company Filed Mar. 8, 1966, Ser. No. 532,639 Claims priority, application Great Britain, Mar. 10, 1965, 10,329/ 65 1 Claim. (Cl. 123-448) ABSTRACT OF THE DISCLOSURE In a spark ignition system, a transistor is turned on by means driven by the engine, and when it is turned on energy is stored in an inductor in series with the transistor. The transistor is turned off when the current flowing in the inductor reaches a predetermined value, and the energy is then transferred to a capacitor, which when the transistor is turned on again is discharged to produce the spark. In series with the transistor is a transformer, and the arrangement is such that as the current through the transistor increases, the transformer applies an increasing base drive to the transistor so as to ensure adequate base current in the transistor as the current in the inductor increases.

This invention relates to spark ignitions systems for internal combustion engines of the kind in which current flow through inductor is controlled by a transistor, the energy stored in the inductor later being used to produce a spark.

According to the invention a drive circuit for the transistor of a system of the kind specified includes means for initiating conduction of the transistor so that current flows through the transistor, and a feedback transformer for increasing the drive current applied to the base of the transistor as the current flowing through the transistor increases.

In the accompanying drawings, FIGURE 1 is a circuit diagram illustrating an example of the invention.

Referring first to the drawing, there are provided positive and negative lines 11, 12 which in use are connected to the battery of a vehicle. Connected in a series circuit across the lines 11, 12 are a storage inductor 13, the primary winding 14 of a transformer 15, a diode 16, a transistor 17 and a resistor 18. A point intermediate the inductor 13 and winding 14 is connected through a diode 19 to one end of the primary winding 21 of an ignition transformer 22, the other end of the winding 21 being connected to the line 12 through a controlled rectifier 23. The winding 21 and rectifier 23 are bridged by a capacitor 24, and the secondary winding 25 of the transformer 22 is connected through a distributor 26 to the plugs 27 of the engine in turn. The anode and cathode of the rectifier 23 are interconnected through the cathode and anode of the diode 28.

The emitter of the transistor 17 is connected through a resistor 29 to the base of a transistor 31 having its emitter connected to the line 12 and its base and collector connected to the line 11 through resistors 32, 33 respectively. The collector of the transistor 31 is further connected to the base of a transistor 34, the emitter of which is connected to the line 12, and the collector of which is connected to the base of the transistor 31 through a resistor 35, and to the line 11 through the primary winding 36 of a transformer 37 having secondary windings 38, 39. One end of the winding 38 is connected to the emitter of the transistor 17, and its other end is connected to the anode of a Zener diode 41 the cathode of which is connected to the base of the transistor 17 through a resistor 42 and a diode 43 in parallel. Moreover, the base and emitter of the transistor 17 are interconnected through the secondary winding 44 of the transformer 15. One end of the winding 39 is connected to the cathode of the rectifier 23, and its other end is connected to the gate of the rectifier 23 through a capacitor 45, a diode 46 and a resistor 47 in series, the capacitor 45 being bridged by a resistor 48.

In order to understand the operation of the ignition circuit, consider a point in a cycle of operation in which the capacitor 24 is charged. At this point, the transistors 17, 34 are off but the transistor 31 is on. At the instant when a spark is required, a pulse is applied to a terminal 49 by any convenient means driven by the engine in timed relationship thereto. The terminal 49 is connected to the base of the transistor 31, and the pulse acts to turn the transistor 31 off, so that the transistor 34 is turned on. Current now flows in the winding 36, and so currents are induced in the windings 38, 39. The current induced in the winding 39 is fed through the series circuit 45, 46, 47 to the gate and cathode of the rectifier 23 to turn it on, and consequently the capacitor 24 discharges through the winding 21 and the rectifier 23. Discharge of the capacitor causes a high to be induced in the secondary winding 25 of the transformer 22, thereby producing the required spark. The resonance of the discharge circuit of the capacitor 24 switches the rectifier 23 oii by reverse biasing it.

At the same time as the rectifier 23 is switched on, the current induced in the winding 38 is passed through the resistor 42 to the base and emitter of the transistor 17. The current flowing through resistance 42 is small, but is suflicient to start the transistor 17 conducting. As soon as the transistor 17 conducts, its collector-emitter current begins to rise, and the current supplied from the winding 38 would not be suificient to maintain the transistor 17 saturated. However, as current flowing through the transistor 17 increases, feedback is provided by way of the transformer 15 to increase the base drive, and so the transistor 17 is maintained in its saturated condition.

Current flowing through the transistor 17 causes energy to be stored in the inductor 13, and when the voltage across the resistor 18 reaches a predetermined value, the transistor 31 is switched on again and consequently the transistor 34 is switched off. An E.M.F. is again generated in the winding 39, but this has no effect on the rectifier 23 because of the diode 46. At the same time, the current is induced in the winding 38 which passes through the diodes 41, 43 to reverse bias the transistor 17 so that it is switched off. The transformer 15 can also assist turn-off. It will be understood that the transistor 17 will be switched oif if its base-emitter current is merely removed, but it is preferred to reverse bias the base-emitter junction in order that the switch-off is rapid. As soon as the transistor 17 ceases to conduct, the energy stored in the inductor 13 is transferred to the capacitor 24 by way of the diode 19, so completing one complete cycle of operation. The voltage to which the capacitor 24 is charged is considerably in excess of the battery voltage.

Because the series circuit including inductor 13 remains completed until the voltage across the resistor 18 reaches a predetermined value, the current flowing through the inductor 13 at the moment when the transistor 17 is switched off will be independent of battery voltage, and so the energy transferred to the capacitor 24 will be constant. Moreover, since the base drive for the transistor 17 is provided by the transformer 15 after the initial drive is received from the transformer, 37, this base drive will also be independent of battery voltage. These two features render the circuit particularly useful in cases where the battery voltage can fall to a very low level.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

3 Y 1. A spark ignition systems for an internal combustion engine, comprising in combination (a) a D.C. source (b) a transformer having a primary winding and a secondary Winding, the transformer having the characistic that as the current flow through its primary winding increases, the current flow through its secondary winding increases proportionately (c) a series circuit connected across said DC. source and including an inductor, the primary winding of v said transformer and the collector-emitter path of a transistor (d) a feedback path coupling the secondary winding of said transformer with the base of said transistor (e) meansoperable in timed relationship with the engine for initiating conduction of said transistor at instants when a spark is required, current then building up in said inductor and said transformer providing increasing base drive to said transistor as said current builds up in said inductor (f) means sensitive to current flow in said inductor for turning said transistor 01f when the current flowing in said inductor reachesa predetermined value (5;) a capacitor coup-led with said inductor where energy stored in said inductor is transferred to said capacitor when said transistor is turned off (h) means for discharging said capacitor when the transistor conducts (i) means operable by discharge of the capacitor for producing a spark.

References Cited UNITED STATES PATENTS 21,847,489 8/1958 Short et ai 123-148 3,263,124 7/1966 Stuerrner 123-448 3,271,593 7/1966 De Vilbiss 307-885 3,302,629 2/1967 Shano 123-148 3,312,211 4/1967 Boyer 123-148 3,318,296 5/1967 Hutton 123-148 LAURENCE M. GOODRIDGE, Primary Examiner 

